TRAINING-RELATED ENHANCEMENT IN THE CONTROL OF MOTOR OUTPUT IN ELDERLY HUMANS

The increase in motor unit force that occurs with aging has been hypot hesized to cause a decline in the ability to maintain a constant subma ximal force. To test this hypothesis, young and elderly subjects perfo rmed a 12-wk strength-training program that was intended to increase m otor unit force. The training program caused similar increases (%initi al) in the training load (137.4 +/- 17.2%), twitch force (23.1 +/- 7.4 %), and maximum voluntary contraction force (39.2 +/- 6.8%) of the fir st dorsal interosseus muscle for the young and elderly subjects. The i ncrease in strength was associated with a modest increase in muscle vo lume (7% of initial value) and a nonmonotonic increase in the surface- recorded electromyogram that was significant at week 8 but not at week 12. The elderly subjects reduced the variability in force at the lowe r target forces (2.5, 5.0, and 20.0% maximum voluntary contraction for ce). This improvement, however, was unrelated to changes in the distri bution of motor unit forces, which was not consistent with the hypothe sis that the greater coefficient of variation for the force fluctuatio ns is due to increased motor unit forces.